How to provide a limited language option to the user.

[eluser]Aken[/eluser]
I did basically what you described on an informational site. You can view it's functionality here: http://f4i.modyourbike.com/specs ("US Measurements | Switch to Metric").

I have a function set up to search the user's session (using CI's standard cookie) and see what language they've selected. By default there's none defined, so it just uses the measurement specified (in this case, US by default).

I have a controller called "setmeasure" set up, and for whichever one is specified, it adds the session variable to the cookie, so it can be called site-wide.

I've also got some fancy nonsense setup using jQuery that shows and hides info depending on which measure is set (sweet for SEO!), but that's not really necessary. More just for me to play with.